1. Field of the Invention
This invention relates generally to absorbent compositions adapted to soak up and retain hydrocarbon liquids.
More specifically, this invention relates to admixtures of particulate solid absorbents with a high molecular weight, hydrocarbon soluble polymer, the mixture being formulated in a manner which allows the polymer to dissolve in the hydrocarbon liquid taken up in the sorbent and to retain the liquid therein.
2. Description of Related Art
A wide variety of organic and inorganic absorbents have been used to soak up oils and other spilled hydrocarbon liquids. Organic materials commonly used for this purpose include straw, wood pulp, saw dust, peanut shells, dried peat fibers, paper, and a variety of similar materials. Probably the most commonly used organic absorbent is saw dust as it has good absorption properties and is widely available at modest cost. Among commonly used inorganic absorbents are diatomaceous earth, expanded micas such as vermiculite, pumice, and similar porous materials.
It is also common to use adsorbents to capture and remove spilled oils and other hydrocarbons, particularly in those cases where the hydrocarbon liquid is associated with or floating on water. Adsorbent materials are distinguished from absorbent materials in that adsorption is a surface phenomenon in which hydrocarbon liquid taken up by the adsorbent material is distributed in film fashion over the surface of the adsorbing material. Absorption, in contrast, is the taking up of the liquid into the body of the solid absorbent material and is associated with the pore structure of the solid.
Adsorbent materials which have been commonly used for the capture of hydrocarbon liquids include fine plastic fibers such as polypropylene wool, a variety of natural fibers including cotton and other plant fibers, cellulose and the like, which have been rendered water repellent through use of a hydrophobic coating and even fine sand, clays and other solid inorganic materials.
One example of absorbent use for liquid hydrocarbon capture is set out in the Ericsson patent, U.S. Pat. No. 4,537,877. The absorbent described by Ericsson comprises a mixture of hydrophobic cellulose pulp fibers with an inorganic filler of the type conventionally used in paper manufacture. The cellulose fibers are rendered hydrophobic by conventional methods such as sizing with resins or prepolymers or by applying a thermoplastic polymer to the fibers by melting the thermoplastic material. According to the inventor, those absorbent compositions disclosed in the patent display a low explosion hazard and low flammability prior to use but, after absorption of oil, are readily flammable and are entirely consumed when burned leaving but a small ash residue.
Adsorbents used for liquid hydrocarbon capture are illustrated by a patent to Tomita et al, U.S. Pat. No. 4,072,794, and by a patent to Sato et al, U.S. Pat. No. 4,206,080. The Tomita et al patent describes an adsorbent which comprises double-coated natural fibers. Fibers useful in the described adsorbent include peat fibers, coconut husk fibers, jute, cotton, wool, hair and the like. The fibers are first coated with a paraffin emulsion and are then dried. In a second coating step, the paraffin-coated fibers are treated with a rubber latex which is thereafter cured to form an elastic rubber surface layer. The purpose of the rubber layer is to protect the paraffin layer and prevent its separation from the fiber or dissolution in the oil. The described compositions are said to provide advantages in that the composition floats on water for long periods of time while retaining its original form and without extraction of paraffin by the oil and the oil-loaded adsorbent burns without problem.
Sato et al describe an oil-adsorbing composition which comprises a granulated mixture of an inorganic filler material which adsorbs oil, the mixture bound together with a cross-linked, oleophilic polymer. The composition is manufactured by mixing and crushing the ingredients while cross-linking the polymer. Suitable polymers are those which are cross-linkable by action of heat or a cross-linking agent and include ethylenic polymers and rubbers. After cross-linking, such polymers ordinarily display little if any solubility in ordinary hydrocarbon solvents.
Both absorbent and adsorbent materials of the prior art tend to have a practical disadvantage. They tend to ooze liquid if loaded anywhere near capacity. The need for sorbent materials which overcome that drawback can readily be appreciated.